Electron gun assembly adapted for a color image receiving tube

ABSTRACT

The focusing characteristic of this electron gun is not impaired by the aberration caused by the deviation from the centers of the holes on both sides of the main lens, through which the electron beams pass, and the astigmatism of the electron beams due to the uneven magnetic field such of a deflecting yoke when the electron gun is in operation. In the focusing electrode 1 of the electron gun a assembly, a plurality of focusing grooves are formed parallel to the direction in which the electron beams pass. A plurality of additional electrode members, each consisting of a flat thin plate, are inserted into the focusing grooves, respectively.

FIELD OF THE INVENTION

This invention relates to an electron gun assembly for a color imagereceiving tube. Specifically, the invention relates to an electron gunassembly which prevents a lowering of the focusing characteristic of acolor image receiving tube from being disturbed by aberrations caused bydeviation of the centers of electron beams through holes of a main lensand by the occurrence of uneven magnetic field phenomena upon electronbeams, such as deflection yoke, during the operation of the electron gunassembly.

BACKGROUND OF THE INVENTION

Generally, a color image receiving tube comprises a panel 11 on which afluorescent film 12 is coated and a funnel 13 attached to the back ofthe panel 11 as shown in FIG. 1. Inside the image receiving tube, anelectron gun assembly 8 emitting thermion and a shadow mask 14distinguishing colors are installed. A deflection yoke 15 is mounted onthe outer surface of the funnel 13 in order to deflect the electronbeams.

The electron gun assembly 8 is comprised of a cathode electrode heatedand operated by a heater, a controlling electrode, a screen electrode, afocus electrode, an anode electrode and a shield cup which are placed inseries in front of the cathode electrode.

Each electrode is placed apart from each other at regular intervals andsupported by bead glass in the shape of a pole or a plate. Eachelectrode has three electron beam passage holes.

Further, at least two electrostatic lenses are formed in the electrongun assembly; one is a pre-focus lens formed by the potentialdifferences between the applied voltage of the screen electrode and theapplied voltage of the focus electrode, and the other is a main lensformed by the potential differences between the applied voltage of thefocus electrode and the applied voltage of the anode electrode. Thepre-focus lens helps prevent the electron beam which emits toward themain lens from scattering, while the main lens converges the electronbeam on the screen.

If the central axis of the electron beam does not impact upon the centeraxis of the main lens, a halo phenomena results at the beam spots on thescreen and the resolution of the color image receiving tube diminishes.

FIG. 2 is a perspective view of the focus electrode used in the priorart for a electron gun assembly. In the electrode body 1, three electronbeam through holes a, b and c are arranged parallel to each other atregular intervals. If both external electron beams converge on thescreen under each of the electron beam through holes of the focuselectrode and the anode electrodes are not in accord with each other, anaberrations occur due to the distortion of the main lens, on theelectron gun assembly of the prior art when both external electron beamsare passing through the main lens, thereby creating a focusingcharacteristic of low quality.

An object of this invention is to provide an electron gun assembly thatprevents the lowering of the focusing characteristic of a color imagereceiving tube caused by the aberration of the electron beam which is inturn caused by deviation of the center of electron beam through holes ofthe main lens and by uneven magnetic field phenomena such as adeflection yoke.

DISCLOSURE OF THE INVENTION

To achieve the electron gun assembly for a color image receiving tubeaccording to the present invention can be improved the focusingcharacteristic on the entire screen since the central axis of theelectron beam through holes in the focus electrode is accord with thecentral axis of the electron beam through holes in the anode electrode.Voltage of a magnitude greater than that applied to the focus electrodeis applied to additional electrode members. Such additional electrodemembers are arranged in parallel with and between the paths of theelectron beams in the focus electrode so that the electron beam isconverged accurately on the screen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a conventional color image receiving tube.

FIG. 2 is a perspective view of a focus electrode according to the priorart.

FIG. 3 is a perspective view of a focus electrode according to thepresent invention.

FIG. 4 shows distribution of electric field around the A--A line crosssection of FIG. 3.

FIG. 5A shows the cross sections of the electron beam passing throughthe main lens of the prior art.

FIG. 5B shows the cross sections of the electron beam passing throughthe main lens of the invention.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention has been described with reference to theaccompanying drawings.

An embodiment of the invention has been illustrated as an electron gunassembly suitable to the separation type of cathode ray tubes, howeverthis invention can be applied to electron gun assembles of other typesof cathode ray tubes as well.

FIG. 3 shows a perspective view of the focus electrode according to thepresent invention. In order to enhance the focusing characteristic ofthe electron beam, focusing grooves 3 are formed on the focus electrodebody 1 in parallel with the path of the electron beam and additionalelectrode members, each consisting of a flat thin plate, 31 and 32 whichare inserted into the focusing grooves 3, respectively.

Two focusing grooves 3 are made on the one surface of the focuselectrode body either on the upper surface, or on the lower surface. Theinvention is not restricted to inserting additional electrode members 31and 32 into the focusing grooves 3, nor is it restricted to theirinstallation in the focus electrode.

The additional electrode members 31 and 32 are preferably rectangular,thin plates of uniform length and breadth. However, they can be made invarious shapes.

The voltage Va is applied to the additional electrode members 31 and 32,respectively and this voltage Va is higher than the voltage Vb appliedto the focus electrode body 1.

Accordingly, when the electron gun assembly is operated, the electronbeam is affected by the electric field formed around the focus electrodeas shown in FIG. 4.

The additional electrode members cause the effect at the four electrodelenses which generates the astigmatism on the electron beam. Suchadditional electrode members generate an electric force which causesoutside electron beams to move toward the central electron beam.

Therefore, since both outside electron beams converge before they passthrough the main lens, the cross-sectional shape of the electron beamaffected by the astigmatism passing through the main lens as shown inFIG. 5B is of greater uniformity than the cross-sectional shape of theelectron beam in FIG. 5A. As a result, the electron beams show lessaberration.

Further, an astigmatism resulting from an uneven magnetic field such asdeflecting yoke is offset by the astigmatism caused by the additionalelectrode members, thereby remarkably improving the focusingcharacteristic around the screen.

Accordingly, the application of dynamic focus voltage to the additionalelectrode members 31, 32, causes the focusing characteristics of theentire surface of the screen to improve remarkably thereby enabling anin-line type electron gun assembly having greater picture definition andhigh picture resolution.

As described above, the present invention has improved the convergenceand focusing characteristics of the electron beam by means of convergingelectron beams before their passage through the main lens. Using plateelectrodes to correct the deviational errors of the electron beam causedby deflection yokes, the present invention has enhanced the focusingcharacteristic of the electron gun assembly.

What is claimed is:
 1. An in-line electron gun assembly adapted for acolor image receiving picture tube having a plurality of electrodes,comprising:a focus electrode body on which focusing openings are formedparallel to an electron beam path, and additional members formed as thinplates and inserted into said focusing openings, respectively, each ofsaid additional members being supplied with a voltage which is higherthan the voltage supplied to said focus electrode body.
 2. A method ofoperating an electron gun assembly adapted for a color image receivingpicture tube having a plurality of electrodes, said electron gunassembly comprising a focus electrode body and additional electrodemembers, said body having a plurality of electron beam through holes anda plurality of focusing openings, each of said focusing openings formedon said body parallel to a respective one of said electron beam throughholes, each of said additional electrode members positioned in arespective one of said focusing openings, said method comprising thesteps of:supplying a first voltage to said focus electrode body, andsupplying said additional electrode members with a second voltage whichis higher than said first voltage.